The invention relates to a cutting device of the type wherein an electrically heated wire extends across a frame for the cutting of plastic materials, particularly plastic foam materials such as porous styrene compounds, and wherein the plastic material to be cut is supported by a plate attached to the frame. The cutting wire is made for example from constantan and is typically dimensioned so that, when the circuit for the wire is closed, the current heats the wire to a temperature ranging from 200.degree. to 300.degree.C thereby enabling the wire to cut said plastic foam material. It has been usual to provide a normally open push-button switch which is manually depressed and must be manually held in depressed position in order to energize the cutting wire; and to deenergize the cutting wire by manual release of the push-button. This arrangement has made it possible to economize the use of electric power incident to the cutting operation. Such arrangement has been fairly successful when the plastic material was stationary and the cutting device, including the push-button switch thereon, was moved manually for the cutting operation. However, difficulty has been encountered in the many, important cases where the cutting device is stationary and the plastic material is manually moved relative to the same. In these cases both hands of the operator are usually needed for properly moving and guiding the plastic material to be cut, but only one hand was available for the purpose, the other hand being needed for closing the push-button switch and holding it closed. This difficulty has interfered with the proper cutting of the desired forms of plastic material, and has particularly made it difficult to cut out of relatively complicated forms.
Another difficulty has been encountered in the use of conventional cutting devices of the indicated type, with push-button switches manually held in closed position. It has happened that the operator, pursuant to placing the plastic material on the supporting plate for cutting this material by the heating wire, forgot the required closing of the circuit for heating the wire. He then contacted the plastic material with the wire, and thereby bent this wire, or in some case even tore it apart.